Pressure-pulse therapy, also known as shock-wave (SW) therapy, is a non invasive extracorporeal technique that is used in many medical applications e.g.: Pulverizing kidney stones and calculi in the bladder and urethra (lithotripsy); Myocardial revascularization in cardiovascular treatments; Cerebral embolism treatment; Orthopedic and sports medicine applications such as rehabilitation of joints, bones, calcifying tendonitis of the rotator cuff, humeral epicondylitis, plantar fasciitis and musculoskeletal problems; Wound healing; Dissolving lipids in cells close to the skin and in the pelvic region, as described in U.S. Pat. No. 3,942,531; Remodeling of the collagen within the dermis using defocused low-energy extracorporeal shock waves (ESW), as was shown by ANGEHRN F. et al, Can cellulite be treated with low-energy extracorporeal shock wave therapy? Clinical Interventions in Aging 2007: vol. 2(4) pp. 623-630; and more.
The shock-wave is generated by an electric storage capacitor that is charged with a very high voltage and subsequently rapidly discharged via an electroacoustic transducer. This electrohydraulic or spark-gap transducer based technique for acoustic shock-wave generation, which is the basis of the present invention, provides for a relatively low cost and compact apparatus. However, the life span of such devices is typically limited to a few thousands of shock-waves due to electrode erosion over a period of use.
Various solutions have been proposed in an attempt to overcome this problem. U.S. Pat. No. 4,730,614 describes a basic solution to the problem of erosion, involving manually adjusting the electrode position. U.S. Pat. No. 6,217,531 describes a solution in which two electrodes are used in the pressure pulse therapy device. As the electrodes become eroded due to use, the distance between the electrodes is mechanically, physically adjusted in order to maintain the original spark gap, or distance between the electrodes. The adjustments are performed automatically. Clearly, manually adjusting the distance between the electrodes is not practical. However, even an automatic control of the mechanical adjustment is not useful because it involves expensive, delicate and complicated equipment. Moreover, mechanical movement of the electrodes can cause other problems, such as improper deviation of the electrode position.
Alternative shock-wave generation method is based on piezoelectric transducer, making use of the fact that polycrystalline piezoelectric ceramic elements expand or, depending on the high-voltage polarization, contract when subjected to a high-voltage pulse. Due to the spherical arrangement of a great number of piezoelectric crystals, the waves thus generated are focused on the center, i.e. the focus, of the spherical arrangement. The advantage of long service life is achieved at the expense of cumbersome and expensive equipment. In addition to this, X-ray localization systems are rather difficult to integrate into piezoelectric systems.
An alternative method is the electromagnetic based system in which a strong pulsed current flows through a flat coil, thus generating a rapidly changing magnetic field. An opposing magnetic field is induced in a metal membrane located above the coil, thus pushing the membrane away from the coil. The initially flat waves are focused by means of a lens array that is arranged above the coil. Also in this method, the longer service life is achieved at the expense of equipment complexity and cost.
An additional drawback of the existing electrohydraulic devices is that in vascular and soft tissue applications, where the chock intensity is relatively limited, the achieved effective therapeutic surface area of the generated shock-wave at the distant focal point within the human body is correspondingly low.